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Based on observations obtained with the Nordic Optical Telescope weinvestigate the spectral variability of the Herbig Ae star RR Tau. This starbelongs to the UX Ori family, characterized by very deep fadings caused by thescreening of the star with opaque fragments (clouds) of the protoplanetarydiscs. At the moments of such minima one observes strong spectral variabilitydue to the fact that the dust cloud occults, for an observer, not only the starbut also a part of the region where the emission spectrum originates. Wecalculated a series of obscuration models to interpret the observed variabilityof the H-alpha line parameters. We consider two main obscuration scenarios: (1)the dust screen rises vertically above the circumstellar disc, and (2) thescreen intersects the line-of-sight moving azimuthally with the disc. In bothcases the model of the emission region consists of a compact magnetosphere anda magneto-centrifugal disc wind. Comparison with observations shows that thefirst scenario explains well the variability of the radiation flux, theequivalent width, as well as the asymmetry of the H-alpha line during eclipses,while the second scenario explains them only partly. This permits us to suggestthat in the case of RR Tau, the main causes of the eclipses are either astructured disc wind, or the charged dust lifted along the field lines of thepoloidal component of the magnetic field of the circumstellar disc.

Modelling UX Ori Star Eclipses based on Spectral Observations with the Nordic Optical Telescope. I. RR Tau